The present invention relates to a multiplexed-information receiving apparatus for receiving, for example, FM (Frequency-Modulated) character-multiplexed information in an FM character-multiplexed broadcast and a navigation system incorporating such multiplexed-information receiving apparatus.
For better understanding of the present invention, the technical background thereof will first be reviewed by reference to the accompanying drawings.
FIG. 8 is a block diagram which shows in general a structure or configuration of a conventional multiplexed-information receiving apparatus known heretofore, by taking as an example an FM radio receiver capable of receiving FM (Frequency-Modulated) character-information multiplexed broadcast services.
Referring to FIG. 8, it is assumed that an FM character-multiplexed information signal which can be derived by multiplexing FM character information, FM speech information and the like in a manner known per se is being broadcast by an FM broadcasting station (not shown in FIG. 8). The FM character-multiplexed information signal is received by an FM (frequency modulation) receiver unit 1. Of the FM character-multiplexed information signal as received, the FM speech information signal component is demultiplexed or separatively extracted to be supplied to a speech output unit 4 to be thereby outputted as speech information in a voice.
On the other hand, the FM character information is sent to an FM signal demodulating unit 2 which is designed to process multiplexed character information. More specifically, the FM demodulating unit 2 serves for demultiplexing or separating multiplexed signal components for performing digital processing thereon with a view to extracting character information of concern. The character information derived from the digital processing executed by the FM demodulating unit 2 is outputted to a display unit 5 via a control unit 3 to be displayed in the form of images or pictures.
FIG. 9 is a block diagram showing generally a structure of a conventional navigation system known heretofore. More specifically, this navigation system is so designed as to be capable of receiving road traffic information. As typical ones of such navigation system, there may be mentioned a system known worldwide as the intelligent transport system (hereinafter referred to as the ITS system) and a system which is known in Japan as the vehicle information and communication system (hereinafter referred to as the VIC system) and which may be considered as constituting a part of the ITS system.
Now, referring to FIG. 9, it is assumed that various service information inclusive of road traffic information is broadcast from a transmitter unit 11 of an infra-information unit 10 incorporated in a system such as, for example, the system known as the VIC system. The service information mentioned above may be broadcast from a central station of the VIC system in the form of character-multiplexed information and picture information. In the navigation system under consideration, the service information broadcast from the infra-information center 10 of the VIC system is received by a receiver unit 6 of the navigation system. The service information as received is sent to a navigation unit 7 from the receiver unit 6. The navigation unit 7 is provided with a database destined for storing map information and others and a global positioning system (hereinafter referred to as the GP system) for obtaining position or location information through the medium of electromagnetic waveform received via a GPS satellite to thereby generate information required for the navigation. Of the information generated by the navigation unit 7, speech information is outputted to a speech output unit 8 while other various service information than the position or location information, map information and the speech information is displayed as a picture or an image on a screen of a display unit 9.
In conjunction with the prior art systems of the structures described above, it is however noted that the FM character information of the FM character-multiplexed broadcast and various service information available from the VIC system are visibly generated on a display screen of the display device in the form of characters, graphics or the like. Further, it is noted that the available amount of such information has a trend to increase more and more. Accordingly, attention of a driver or operator driving a motor vehicle equipped with a navigation system compatible with the VIC system, by way of example, is apt to concentrate his or her attention to the display generated on the display unit when he or she desires to acquire an increasing amount of the information, which is of course undesirable from the standpoint for ensuring the security or safety of the driver.